Iitjminotts dischabge device



May 26 1931. L. DE FOREST LUIINOUS DISCHARGE DEVICE avwwnto'c Lea DeFZHYST- 351 his Gam 11s Filed Aug. 8, 1928 Patented May 26, 1931 UNITEDSTATES PATENT OFFICE LEE m: FOREST, 0! NEW YORK, N. Y, ASBIGNOR '10DEIOREB'I. PHONOI'ILM CORPORA- TION, OF NEW YORK, N. Y., A. CORPORATIONOF DELAWARE LUMINOUS DISCHARGE DEVICE Application filed August 8, 1928.Serial No. 298,210.

This invention relates in general to improvements in the construction ofluminous discharge devices, such as are employed In photographicallyrecording sounds One of the objects of this inventlon is theconstruction of a cathode for luminous discharge devices, by means ofwhich the amplitude of the higher sound harmomcs when 1n the form oflight are exaggerated.

A further object of this invention involves the construction of acathode for luminous discharge devices of particular shape in order toinsure suflicient light fluctuation to produce exaggeration ofthe soundharmonics represented by the fluctuating light.

A still further object of this invention 1nvolves a cathode for aluminous discharge device of such construction that the cathode iscovered for substantially one half of its length under normalexcitation, so that the extent of illumination which is fluctuating inaccordance with sound waves being recorded will not vary sufliciently toentirely leave or cover the cathode.

These and other objects as will appear from the following disclosure aresecured by means of this invention.

This invention resides substantially in the combination, construction,arrangement and relative location of parts, all as will appear.

more fully hereinafter.

Referring to the drawings in which the same reference numerals will beused to indicate the same or similar parts in the different views,

Figure 1 is an elevational view of an old type of luminous dischargedevice.-

Figure 2 is an elevational view of a later improvement thereof.

Figure 3 is a diagrammatic representation of one method ofconnecting'the luminous discharge device to an audion amplifier system.

Figures 4 to 9, inclusive, are elevational views of different forms ofluminous discharge devices embodying the principles of this invention,as illustrated by the different form of cathodes. The portion of theelectrode covered with glow is indicated by the legend G,

tive glow varies in Figure 10 is a diagrammatic illustration of the typeof sound record secured for luminous discharge devices kn own beforethis invention in which practically none of the higher harmonies appear.

Figure 11 is a diagrammatic illustration of a sound record, which hasrelatively flat tops and blank spaces, produced by known luminousdischarge devices having a cathode of regular shape, such as forinstance, as that shown in Fig. 1.

Figure 12 is a diagrammatic illustration of a sound record in which thehigher harmonics are not sufliciently pronounced, so that the record ofthe higher harmonics shows rounded tops. Such a record is produced byuniform cathodes of the form shown, for instance in Figure 1.

Figure 13 is a diagrammatic illustration of a sound record produced bymeans of the device of this invention, in which the harmonics areexaggerated and show pointed tops.

As is well known in this art, there are two general forms of luminousdischarge devices when judged in accordance with the form of soundrecord they produced. With one type the cathode is entirely covered withnegative glow and when the device is operating for the purpose ofrecording sound waves this negaintensity. In the other type of luminousdischarge device the cathode is not entirely covered with negtive glowand when the device is operating to record sound the extent which thecathode is covered with negative glow varies in accordance with thesound waves being recorded.

This invention is particularly related to the form of .luminousdischarge device in which the fluctuation in the extent of glow over thecathode is employed rather than the fluctuation in intensity thereof.

There has long been known in the art a glow lamp similar to the oneshown in Figure 1, where one electrode 2, the anode, is in the form of acircular plate Within an evacuated vessel 1, and the other electrode 3,the cathode is in the form of a long, thin and highly polished strip ofmetal preferably of nickle. As shown the axis of the long electrode 3lies in the plane at right angles to the plane of the electrode 2 andarranged so that the two electrodes are separated by a very smalldistance. It is usual to provide the vessel of such a device with afilling of the proper gas at the proper pressure, as for example,nitrogen at seven or eight millimeters of mercury pressure.

When the device is thus constructed a visible glow will extend from theend of the cathode 3 nearest to the anode 2 down over a portion of thesurface of the cathode. The area of the cathode which is thus covered bythe glow is directly proportional to the current passing through thetube. In other words, if a certain potential is impressed across theelectrodes the visible cathode glow will extend for a certain distance,say for onehalf inch over the surface of the cathode. If the potentialacross the tube is then increased a certain amount so that the amount ofcurrent passing through the tube is increased a definite amount, saytwenty percent, then the area of the illuminated portion of the cathodeis also increased twenty percent. It is understood that a definitedirect potential is constantly impressed across the tube so at all timethere is a portion of the cathode surface illuminated. This type of tubeis known to physicists as a Gehrcke tube.

In the best practice in order to con fine the glow to one surface of thecathode only, which is important for photographically recordingelectrical flucutations, the lower side of the cathode'*and the edgesalso are usually protected by mica, or enameled. It may be pointed outhere as is apparent from the drawings that the surface or outline of the*cathode 3 is uniform.

A more recent development of this type of tube due to Gehrcke in whichthe cathode is in the form of a fork consists of two strips of metal 3arranged parallel to each other and extending longitudinally of thevessel 1 terminating a short distance from the electrode 2. As beforethe surface of the cathode strips 3 are covered with a suitableinsulating material as shown at 4, so that they are only exposed on thetwo adjacent sides which extend parallel to each other. The strips 3 areseparated a short distance, as for example, one or five tenthsmillimeter. With this construction, the cathode glow is limited to thenarrow space between the two exposed polished metal surfaces and isthereby sharply limited as to thickness and also somewhat intensified.The glow has been shown as extending to the point indicated by theletter A. This may for example define the limit of glow under a normalexcitation when it is not being varied by sound fluctuations.

In making photographic records of this type of glow light oscillographit is necessary to place the tube in the camera, so that the long axisof the tube is parallel to the plane of the moving film or photographicplate on which the photograph of the oscillatmg low light is being potographed and exten ing transversely thereof.

Figure 3 illustrates diagrammaticall one method of connecting theluminous disc ar e device to the audion amplifier. The amp ifier isindicated at 5 having a plate 6 connected to the cathode 3. A filamentis shown at 8 energized by the current source 9. The output from themicrophone or other device for changing sound waves into electricalvariations is connected to the grid 7 and the filament 8. A source ofhigh potential is indicated at 10 and is connected at one terminal tothe filament 8 and at the other terminal to the electrode 2 through thevariable resistance 11. The source 10 is a direct current source andsupplies energy for the glow lamp. The current variations from themicrophones are amplified by the audion 5 and impressed upon the glowlight to vary its luminosity, (which is normally constant) in accordanceWith the sound waves. It is to be remembered that in this type ofdevice, the extent of the glow on the cathode varies in accordance withthe fluctuations caused by the sound currents from the amplifier. Inother words, the point A (Figure 2) is moving back and forthlongitudinally of the oathode 3 inamount depending upon the stren h ofthe currents representing the sound being recorded.

As a variation, from the method of direct connection between the audionam lifier and the glow lamp the glow lamp may coupled to the output ofthe audion amplifier either by a resistance, impedance or capacitycoupling as is well known in the audion amplifier art. In all such casesan additional source of electromotive force must be employed forsupplying the direct current normally flowing through the glow tube orphotion oscillograph. When the glow tube is in seri s with the anodecircuit of the amplifier tube the amount of plate current passingthrough the amplifier 2 is limited bythat which the photion is designedto carry. The tube therefore must be designed, so that the normalcurrent which lights half the cathode surface meets the requirementsunder which the amplifier tube best operates. When this is the case,however, the electromotive forces impressed across the two in series isthen regulated until the glow light covers the oathode up to the middleline thereof as has been described in connection with Figure 2 and willbe more particularly pointed out in connection with the other figures.

As indicated thistype of Gehrcke oscillator has previously been used forrecording high frequency electrical oscillations and sound vibrationswhen translated into electrical current. It is not intended to lay anyclaim to the invention of this type of tube per se, or its applicationto sound photography.

The feature of this invention resides in'the fact that I have discoveredthat with certain shapes of cathodes, it is possible to automaticallyemphasize or exaggerate the excursion of the glow back and forth alongthe surface of the cathode, and in a useful way, so as to therebyadvantageously exaggerate the photographic record of certain soundfrequencies over certain illuminated areas, which represent definitedegrees of sound volumes. For example it has long been known in soundrecording whether by phonograph or by photographic means that the higherharmonics are recorded and reproduced with relatively less intensitythan are the low frequencies and fundamentals of sound waves. It ischiefly on this account due to the partial or complete suppression ofthe higher harmonics, that the quality of reproduced sound is so farinferior to the original.

Because there is so little energy in the waves represented by the higherharmonics, it is the purpose of this invention to devise a glowdischarge device employing a cathode of such construction that thehigher hari nonics are exaggerated to overcome this deect.

I have found that by suitably shaping the cathode of the type of tubejust described as shown in Figs. 4 to 9, inclusive, I am able toexaggerate or diminish as desired the photographic record of this soundwhen the volume of the sound as interpreted in electric currents appliedacross the electrodes of the tube is such as to brin the cathode glowover the certain portion 0? the cathode. For example, in Figure 4, Ihave shown the cathode strip 3 narrow at its center, very wide at itstwo ends and tapering in both directions away from the center, which isthe narrowest portion. In the form shown in Figure 5, the cathode 3 isnarrowest at its center and increases in width towards the ends in alinear ratio. The cathode in Figure 6 is of a constant width at thecenter for a short distance and then increases rapidly in width towardseach end in a linear ratio. The cathode in Figure 7 is again narrowestat the center and increased. in width therefrom to each end to form acircular outline or following a sine curve or exponential law.

In the arrangement of Figure 8, the cath- .is shown of constantwidthintermediate the finds. At one end the width increases very rapidlyaccording to a linear function and at the other end increases along acurved line for a distance and then continues at a constant width to theend.

The advantage of having one or both ends of the cathode of large area isthat with such an arrangement no matter what variations of current maybe impressed across the tube the discharge will never seek either toextend beyond the limits of the cathode or to withdraw therefromentirely. Either one of the above effects would be regarded in thephotos graphic film as the equivalent of a blast or overloading of thesystem and would be represented as shown in the record in Figure 11, asflat top waves or of blank spaces in the record. Reproduction of soundsfrom such a record would be very imperfect.

The voltage normally impressed across the tubes to initially energize itshould be such that when no sound is being recorded, the limiting lineof the glow discharge lies substantially in the center of the cathode ashas been indicated at A in various figures. When the current passingthrough the tube increases or diminishes in accordance with soundvariations the travel of the delimiting line A of the cathode glow,right or left, is obviously much more rapid where the cathode is narrowthan in the wider portions.

For example, employing a cathode of the type shown in Figure 6, theexcursions of the glow, right and left of normal position is very rapiduntil the points where the electrode begins to widen are reached,whereafter, the movement right and left of the edge of the cathode glowis slower. This means that in the lower range of sound intensity theamplitude of the light excursions are exaggerated relatively .to whichthey are in the higher ranges of sound intensity. In other words, thephotographic reproduction of weak sound intensities is proportionallybetter than for the large sound intensities. The idea is perhaps moreclearly expressed in Figures 12 and 13.

Figure 12 represents a photographic rec- 0rd from; a tube employing acathode of uniform cross section. It represents a fundamental sound waveembellished by-various harmonics. monic peaks are rounded, which is notconducive of good sound reproduction.

Figure 13 shows a record of the same sound wave from a non-uniformcathode, such as that shown in Figure 6. It is noted that the harmonicof lower sound volume in Figure 12 are more comprehensive than those inFigure 13 although the amplitude of the fundamental is the same in bothcases. Experience teaches that it is necessary in order to secure asperfect sound reproduction as possible, that the higher'harmonics shouldbe exaggerated relative to the fundamental in the record.

It is pointed out that the har- In-a certain type of sound for examplefrom certain forms of musical instruments or of musical compositions, itmay be desirable to overemphasize the harmonicsor the glow lightexcursions representing these at the extremes of the excursion of theglow light. In other words, the sound volume is large relative to therecord obtained when the sound volume is small. For this purpose acathode shaped as shown in Figure 8 is employed. Normally the excursionof the cathode glow should not extend right and left beyond the ointsdetermining the ends of the curved line, but should an exceptionallyloud sound he recorded the sudden enlargement of the cathode area at theends thereof insures that the excursion of the cathode light will notextend beyond the limits of the cathode. This is because the much largerarea at the two ends insure that the cathode light travels relativelyvery slowly as it approaches either end of the cathode. As a result in aphotographic record the peaks of the wave, high or low, will be therebysubdued and rounded off rather than extend beyond the limit of thephotographic track, which would result in a square topped wave asillustrated in Figure 11, with a consequent introduction of falseharmonics and bad reproduction resulting therefrom. For certain types ofsound records it may even be desirable to make the record quiteasymmetric relative to the central or normal position of the glow lightboundary line when no sound is being recorded.

An arrangement for accomplishing this result is shown in Figure 9, wherethe excursions to the left of the normal position are relatively smallcompared with the exaggerated excursions of the light limit above thenormal position. This arrangement results in exaggerating the peaks ofthe photographic record, and minimizes the valleys below the medium lineof the record. Also the cathode can be reversed so that the narrowposition extends towards the anode and the broad portion away from thesame. Such an arrangen'ient as this results in a photographic recordwhere the valleys of the graph are exaggerated below the medium line andthe peaks above the medium line are diminished.

For the ordinary recording of the sound I have found that asymmetrically distorted shape of cathode such as those shown in Figures4 to S, inclusive is preferable.

As referred to in connection with Figure 2, the cathodes in the variousforms shown in Figures 4 to 9, inclusive may be provided on one sidewith an insulating material, such as mica or enamel to confine the glowto one surface only. It is also to be distinctly understood that in theforms of devices shown in Figures 4 to 9 inclusive, that two metalstrips 3 of the same shape may be disposed parallel to each other andseparated b a small distance, in the manner indicate in the constructionin Figure 2.

It is obvious that various applications of the principles which I havehere explained may be made so that the photographic sound record may bedistorted in anyway that may be found desirable, by simply so shapingthe cathode area as to produce the desired distortion in thephotographic record. The chief advantage of the method which I haveoutlined is to emphasize the higher harmonics of the recorded soundwhich are normally of relatively low intensities, and are as aconsequence inadequately recorded and inadequately reproduced by thereproducing system, particularly the loud speaker elements thereof.

I do not therefore desire to be limited to the physical formsillustrated in the disclosure, but rather to any form of deviceemploying the principles of this invention and particularly to the scopeof the invention as it has been defined in the appended claims.

What I seek to secure by the United States Letters Patent is:

1. In a glow light for use in photographically recording sound waves thecombination comprising an evacuated vessel, an anode in said vessel anda cathode of uniform thickness, the width of which varies along itscentral axis so that a varying voltage across the electrodes willproduce a varying negative glow which is exaggerated.

2. A sound recording glow light of the variable extent of glow areatype, comprising an evacuated vessel, an anode and a cathode consistingof a fiat plate or strip of constant thickness, the width of whichvaries along the central axis thereof so that the varying glow thereonwill be distorted.

3. A sound recording glow lamp of the type described comprising anevacuated vessel, an anode, and a cathode comprising two parallel stripsof metal of uniform thickness and of varying width facing each other andseparated by a distance which is small relative to the width of thecathode strips.

4. In a sound recording glow light of the type described the combinationcomprising a vessel and anode in said vessel and a cathode of varyingwidth so as to produce irregular tube in which the negative glow variesin extent, a cathode consisting of a metal strip varying in width alongregular lines from the center to the ends, so that the ends are of thegreaterwidth.

.8. In a sound recording glow discharge tude in which the negative lowvaries 1n extent, a cathode consisting 0 a metal strip varying in widthalong regular lines from the center to the ends so that the cathode isthe Widest at least at one end.

9. In the method of making photographic sound records with a glowdischarge, the step of'varying the extent of the glow discharge so as toexaggerate its amplitude of variation in certain known and predeterminedportions-of its movement, independent of the relative amplitude of theoriginal sound Waves being recorded.

10. In the method of making photographic sound records with a luminousgas discharge device connected to the output of an amplifier whichitself may produce distortion, the steps of varying the luminousdischarge of the device independent of any distortion produced by saidelements in a degree either less than or greater than the degreeproportional to the varying sound currents causing the variation.

11. A sound recording glow light of the type described comprising anevacuated vessel, an anode and a cathode in said vessel, said cathodevarying in width from its center towards both ends.

In testimony whereof I have hereunto set my hand on this 30th day ofJuly, A. D. 1928.

LEE DE FOREST.

